recording vocals

For delay times, here is a quick overview –
0-15/20 ms is not distinctly discernible and manifests as a timbre change (comb filtering kicks in early and begins to drive the timbre down). This area is good to play in to understand how the sound changes with adjustment.
20-50 ms is just discernible, and manifests as a “doubling” effect (this is where “chorusing effect” kicks in).
50-150 ms are easily discernible and sound as rapidly decreasing echoes (or “slapback echo”).
>150 ms delivers highly defined echoes (not often useful for voice, depending on application).